Comparative Analysis of Circular and Linear mRNA Vectors: Expression and Immunization

Overview

This study compares the expression efficiency and immunization efficacy of circular and linear mRNA vectors. Modified linear mRNA vectors demonstrated significantly higher protein expression in vitro and in vivo, while both vector types showed comparable immunogenicity and protection in active immunization models. Linear vectors provided superior protection in passive immunization correlating with their higher protein expression.

Background

mRNA vaccine technology offers rapid, scalable production and has been pivotal during the SARS-CoV-2 pandemic. Two main mRNA vector types exist: linear (cap-dependent) and circular (cap-independent), each with unique advantages. Linear vectors, widely used in approved vaccines, rely on cap structures and untranslated regions for expression efficiency. Circular vectors depend on internal ribosome entry sites (IRES) for translation and have shown promise against various viral pathogens and cancer. Despite advances, comprehensive comparisons of optimized vectors for expression and immunogenicity have been limited.

Data Highlights

Key Findings

• Modified linear mRNA vectors with N1-methylpseudouridine and CleanCap capping exhibit significantly higher protein expression than circular vectors.
• Both circular and linear vectors induce similar immunogenicity and protective efficacy in active immunization against SARS-CoV-2 challenge.
• In passive immunization models requiring high protein expression, linear vectors provide superior protection compared to circular vectors.
• Circular vectors tested included IRES elements from coxsackievirus B3 and a novel human rhinovirus B6, with comparable immunogenicity but lower expression than linear vectors.
• Linear vectors capped with advanced CleanCap reagents outperform those capped with first-generation ARCA analogues in expression efficiency.

Clinical Implications

For vaccine development targeting active immunization, both circular and linear mRNA vectors can be effective, allowing flexibility in vector choice. However, for applications requiring high protein expression such as passive immunization or recombinant antibody production, linear mRNA vectors with optimized modifications are preferable. Understanding vector-specific expression and immunogenicity profiles can guide tailored vaccine and therapeutic design.

Conclusion

While modified linear mRNA vectors achieve higher protein expression, circular vectors provide comparable immunogenicity and protection in active immunization. Linear vectors are advantageous for passive immunization strategies requiring elevated protein levels.

References

1. Wan J et al. 2022 -- Immunogenicity comparison of linear and circular mRNA vectors
2. Qu L et al. 2023 -- RBD-domain based mRNA vaccine efficacy
3. BNT162b2 Vaccine Studies -- mRNA vaccine technology and CleanCap capping